The natural development of multiple-flow turbojet engines that have a fan, in particular upstream, is to increase propulsive efficiency via a reduction in specific thrust, which is obtained by reducing the pressure ratio of the fan, which is manifested by an increase in the bypass ratio (BPR), which is the relationship between the mass airflow through one or more than one of the ducts surrounding the gas generator by the mass airflow through the gas generator, calculated at maximum thrust when the engine is immobile in an international standard atmosphere at sea level.
However, the increase in the bypass ratio has an influence on the diameter of the turbine engine which is constrained by the requirement to allow a minimum ground clearance because of the fact that the turbine engine is most often integrated under the wing of an aircraft.
One solution consists of assembling more than one fan on at least one offset axis, i.e. not coaxial with the axis of the turbine engine, in order to increase the bypass ratio while maintaining an appropriate ground clearance under the wing of the aircraft. However, this architecture has an impact on the mass of the turbine engine, in particular because of the weight of the casings enveloping each fan. The fan casings surround the fan vanes and are connected to the gas generator by stator vanes known as outlet guide vanes (OGV). These stator vanes are disposed downstream of the fan vanes and enable the flow generated by the fan to be straightened. These vanes are disposed radially from the axis of rotation of the fans.
The fan casings can also carry thrust reverser systems that enable the thrust of the secondary flow generated by the fans in the landing phases to be reversed in order to facilitate the braking of the aircraft and to reduce the braking distances. This thrust reverser system as described in document US 2015/113945 is in great demand by aircraft manufacturers and also by pilots in order to be able to adapt to any type of landing runway.
A conventional bypass turbine engine is equipped with a thrust reverser system, which is installed downstream of a nacelle incorporating the fan casing. This thrust reverser system generally comprises a plurality of doors that pivot towards the exterior of the nacelle and which have the disadvantage of increasing the length of the nacelle and increasing the mass of the propulsion assembly.
The integration of this thrust reverser system into multi-fan turbine engines further penalises the mass of the propulsion assembly because the number of doors is increased and limits its integration with, for example, adjacent fans.